The colonisation of treated water systems by Legionella pneumophila

Rogers, Julie (1994). The colonisation of treated water systems by Legionella pneumophila. PhD thesis The Open University.



A two-stage continuous chemostat model of a water system was developed to investigate the ecology of L. pneumophila. The inoculum was derived from a calorifier responsible for an outbreak of Legionnaires' disease and contained virulent L. pneumophilaa serogroup 1 along with associated microorganisms including protozoa. The model system was supplied with filter sterilised tap water as the sole nutrient source for the growth of the mixed microbial population and was used to investigate both planktonic and attached growth.

The characteristics and reproducibility of biofilm formation on glass surfaces were examined and this provided insights into the three dimensional structure of biofilm formation. Examination of the biofilms using immunogold labelling techniques demonstrated that cells of L. pneumophila were present within the biofilm as microcolonies, this could indicate that the pathogen could grow extracellularly by receiving nutrient from the bacterial consortium.

The influence of plumbing material selection on the growth of L. pneumophila was investigated using the model system. The results obtained indicated that copper was an inhibitory material in terms of both biofouling and the growth of L. pneumophila. Latex and ethylene-propylene which are used for sealing plumbing systems were found to be nutrient supplying materials. These elastomeric materials supported extensive biofilms after only 24 hrs and contained high numbers of the pathogen. Steel and plastic materials supported biofilms which were intermediate in terms of total biofouling and growth of the pathogen.

The influence of water temperature on biofilm formation and the inclusion of L. pneumophila was also investigated. At 20 °C and 50 °C L. pneumophila was present in biofilms in low numbers. At 40 °C L. pneumophila was present in the planktonic and biofilm phases in high numbers and accounted for as much as 50 % of the biofilm flora. At 60 °C the pathogen was absent from the model system. Copper was found to be inhibitory to colonisation and growth of L. pneumophila.

The model system was used to develop biofilms on the surface of appropriate plumbing materials and then these were used to determine efficiency of commercially available biocides. The results demonstrated that attached bacterial populations were more resistant to biocide treatment than the planktonic phase. However, even the planktonic populations were able to survive the recommended biocide doses suggested by the manufacturers. The implications of the data on the ecology of the pathogen is discussed in relationship to the prevention of infection. The data provides additional information on the dynamic relationship which exist within biofilms and gives additional understanding on biofilm formation.

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